Electrical musical instrument



Oct. l2, 1954 J. M. HANERT ELECTRICAL MUSICAL INSTRUMENT 2 Sheets-Sheet 1 Filed June 25. 1950 0N m M NC. fr DF mp. QP h... G... ML. ,WP m. NF F LLL . WDMOIU HD7/i2 u mJQmmolATll. l|

DNOIU Oct. l2, 1954 J. M. HANERT ELECTRICAL MUSICAL INSTRUMENT 2 Sheets-Sheet 2 Filed June 23, 1950 MC. C 0:. L mm @zu EL@ NSN nu" MWA MJ NEN .wN WUI GMC .00.

WMPO 2 .NOK NOlQJJ UmmU Ew @whim Patented Uct. 12, 1954 ELECTRICAL MUSICAL INSTRUMENT John M'. Hanert, Park Ridge, Ill., assigner to Hammond Organ Company, a corporation of Delaware Application June 23, 1950, Serial No. 169,892

6 Claims. l

My invention relates generally to electrical musical instruments and more particularly to an improved instrument of the electric organ type.

It is now well-known that electric or electronic organs may be built using various types of electrical tone signal generators such as electronic oscillators, vibratory reeds, rotating magnetic tone wheels or phonic wheels, photoelectric generators, rotary and vibratory capacity pickup generators and others. The art has progressed to a point of development where the problems encountered by manufacturers of instruments of these types are not primarily concerned with the provision of improved tone signal generating and control means but rather with the production of an instrument oi this character at the lowest possible cost.

Generally speaking, an electrical musical instrument of the organ type which shall be capable of playing popular music, homophonic music, and all except contrapuntal music, should have a range of at least two octaves, plus five notes throughout which the melody may be played, a range of two octaves for the production of the accompaniment chords, and a range of at least one octave for the production of the bass or subbass tones. This adds up to a total range of about ve and one-half octaves or about sixtyfive semitone intervals.

It has been the general experience of manufacturers of instruments of this type that the cost of production of such instruments increases in part proportionately with the number of signals of different pitches which the instrument shall be required to produce. This conclusion is based upon the consideration that the elements or components of the instrument which are pitch determinative are the more expensive parts of the signal generating apparatus of the instrument, since such parts and components must be made with a reasonably high degree of precision so that over a long period of time they will maintain their pitch reliably, preferably within one part in three hundred, or at most, within one part in two hundred.

It is an object of my invention to produce an electrical musical instrument of the organ type in which the number of pitch determining instrumentalities or components is greatly reduced as compared with the number required in present instruments. For example, electrical organs in the past have conventionally employed at least sixty pitch determining instrumentalities for the production of theitones of the melody and of the accompaniment, and at least twelve additional pitch determining components for the pedal bass (ci. iii- 1.61)

tones, making a total of atleast seventy-two pitch determining components. In the piano there may be as many as 176 strings, and frequently more, because, except for lowest notes, there are at least two strings and sometimes three strings per note.

in the past inventors have proposed reducing the number of pitch determining components of the instrument, for example, by using a single oscillator tunable to either of two semitone frequencies, thereby reducing by one-half the number of pitch determining components required for an instrument of given pitch range. In other prior art instruments it has been proposed to produce all of the pedal bass tones by means of a Single oscillator tunable to any of the semitcne pitches within the pedal bass range.

I have discovered that it is possible to provide an electrical musical instrument usable by the player to play all popular and homophonic music in the conventional manner utilizing at the most seven oscillators for determining the pitch of all of the notes played. Further, the number of oscillators may be reduced to five if it be conceded that itis not essential to be able to produce the seldomly appearing 9th chord in the playing of such popular and homophonic music.

By thus reducing the number of oscillators te a small fraction of the number conventionally considered essential for determining the pitch of the tones produced by an electrical musical .instrument of the organ type, and with the addition of but a few relatively inexpensively produced components, the over-all cost of an instrument of this character may be very substantially reduced. The primary object of the invention is theren fore to provide an electrical musical instrument on which it is possible to play popular and homephonic music and which has a minimum number of oscillators.

Other objects will appear from the foliowing description, reference being had to the accompanying drawings in which:

Figure 1 is a diagrammatic representation of the 'manner in which popular music is played on an instrument of the organ type;

Figure 2 is a diagrammatic illustration of the manner in which the chord and pedal tone determining switches are operated by accordion type key buttons; and

Figure 3 is a schematic block and wiring diagram of a representative form of the simplified improved instrument of my invention.

As an illustration of the manner in which popl ular music is scored and the manner in which it is played on an instrument of the organ type there is shown in Fig. l the first six measures of a popular musical score, Home On The Range. It will be noted that the notes of the melody are scored in the conventional manner and, according to generally accepted convention, the accompaniment chords are indicated by key letter notations directly above the staff.

In Fig. l it will be noted that above the first note of the fourth measure there is an indication Bb, which to the musician means that the accompaniment chord to be played is the Bb major chord. Similarly in the second and last measures of the portion of the score the letter' F above the staff indicates to the musician that the F major accompaniment chord is to be played at the beginning of these measures. The other conventional chords such as the minor, 7th, diminished, augmented, minor '1t.i, 9th, and major th are similarly scored giving the key of the chord followed by the notation m, '1, m?, 9, and 6. These chord designations dc not require that the musician play certain notes but require that he play the notes of that chord in any of its inversions. It also indicates to him that he should play one of two or possibly three bass pedal notes.

For example, in the illustration selected, the Bb major chord called for in the fourth measure of the score could be played by the musician by depressing keys B'o2, D3, and F3, or the musician might prefer to play the second inversion of this chord, namely, the notes F2, BUZ, and D3, or he may play the first inversion in the lower octave, namely, the notes D2, F2, and Bb. These three ways of playing the chord are equally correct, and each is an accurate and faithful rendition of the music as scored.

in the pedal register the musician may depress the Bbl) pedal to obtain the root, or FQ pedal, to obtain the ilfth in the next lower octave. In some instances the F1 pedal of the organ might be preferred by the musician. However, playing the root of the chord in the pedal register is always proper and musically acceptable.

From the foregoing it will appear that the music as scored may be correctly rendered by the musician in a number of different but similar ways. equally correct ways in which all the diierent chords in the twelve keys may be played shows that all of these chords may be played by depressing keys within the range of F2 to Similarly all of the sub-bass root notes may, and customarily are, played on the pedals Within the range of FO to El.

The melody or solo portion of the score of practically all popular homorphonic music is scored and may be played within the range from C3 to F5.

Considering the foregoing characteristics of popular and homophonic music and the manner in which it is scored-and played I have discovered that all of such music may bc rendered adequately by the use of but ve oscillators if it be not required that the 9th chords be played, and that with the addition of but two oscillators the 9th chords may also be played.

An instrument of the type employing only five oscillators is schematically illustrated in Fig. 3 as comprising a solo oscillator itl and four chord oscillators II, I2, S3, and I4. These oscillators may be of any well-known type. The solo oscillator it is illustrated as comprising a pair of A consideration of the different but triodes IB and I9 which are preferably in a single envelope. The resonant circuit for determining the frequency of oscillation comprises a single capacitor C29 and a plurality of separate inductances L22 connected in series between the grid 2li of triode I3 and ground. The junction points between the inductances L22 may be connected to a grounded conductor 30 by closing switches 26. These switches are operated by keys Dbl? to F5 respectively. There is no switch 26 provided or the key C3 so that the oscillator will oscillate at the pitch of C3 whenever none of the other keys is depressed. The key C3, however, and the keys Db3 to F5 operate switches 32 respectively, which upon closure connect the grounded conductor 30 to a conductor 34 which, as will appear hereinafter, forms part of the circuit for controlling the output of the oscillator.

The cathode 36 of triode I8 is connected to ground through arself-biasing resistor R43, and its plate 42 is connected to a terminal of the power supply, indicated as a B+ terminal, through a load resistor R44. The plate 42 is also coupled to the grid 46 of triode I9 through a blocking capacitor C48 and a limiting resistor R50, the junction between C455 and .R50 being connected to ground through R52. The cathode 54 of triode i9 is connected to ground through a cathode load and self-biasing resistor R56. Plate current is supplied to the triode i9 from a suitable B+ terminal of vthe power supply through a load resistor R58, the plate 60 being connected to the grid 24 through a feedback circuit comprising a capacitor C62 and a resistor R64.

"he signal is derived from the cathode 54 of triode i9 through a capacitor C66 which is in series with a decoupling resistor 'R68 and the primary winding L10 of a transformer 12.

The secondary winding L14 of this transformer has its terminals respectively connected to the grids of control triodes 1G and 18. A center tap on the secondary winding L14 is connected to ground through an attack and decay capacitor C and is normally connected to a suitable source of biasing potential, indicated as a terminal C-, through a decay resistor R82. The center tap is connected to ground through an attack resistor R84, conductor 34, one of the switches 32, and conductor 30 whenever one of the playing keys is operated.

The cathodes of the triodes 16 and 18 are connected to ground while their plates are connected to the terminals of the primary winding L86 of transformer 81, the-center tap of the primary being connected to a B+ terminal of thepower supply. The secondary winding L88 has one terminal connected to ground and its other terminal connected to the input terminal of an ampliner 90 through a volume controlling adjustable resistor R92.

The potential on the C- terminal is sufficiently low to bias the triodes 16, 13 beyond cutoi, but the resistor R84 is of sufficiently lower value than the resistor R82 that upon closure of one of the switches 32 the potential on the grids of triodes'16 and 18 is raised Vsuihciently to render these triodes capable of conducting the signal. The rate of change in gain, and hence the character of the attack portion of the tone signal envelope, is determined jointly by the values of C80 and RS4 while the decay portion is determined jointly by the values of CBI! and R82. The melody instrument thus described is exemplary of an electronic melody or solo type instrument in which there is'v but a single oscillator which determines the pitch of the tones produced.

The chord oscillator II is capable of providing tone signals of pitches F, Ft, G, and Ab. It comprises a triode It@ having an oscillation frequency determining resonant circuit which includes a capacitor CI02 and a center tapped inductance LIM. One terminal of the inductance LIM is connected to ground while the other terminal is connected to the grid of triode I through a grid leak resistor Ritt which is bypassed by a capacitor CIOS. Plate voltage is supplied from a B+ terminal of the power supply through a load resistor RI Ill, and the cathode is connected to the center tap II2 of inductance LIM. This oscillator is a. conventional Hartley oscillator. To enable it to provide different frequencies three capacitors CI I4, CI I5. and CI I6 are connected in series, and one or more may be connected in parallel with a portion of the inductance Lili@ upon closure of tuning switches TI, T2, or T3. It will be clear that when the switch TI is closed the capacitor CI It is connected between ground and the center tap II2 and that as a result the frequency of the oscillator is reduced. The value of capacitor CI I4 is such that the pitch of the oscillator is lowered three semitones from its normal Ab pitch to the pitch of the note F. Similarly when switch T2 is closed capacitors CIId and CII are connected in series between the tap I I2 and ground, and the value of the capacitor Cll is such that the pitch will be lowered to seinitones, from Ab to Fit. Likewise when the switch T3 is closed the three capacitors CIM, CI I5, and CI I6 are connected in series between tap II2 and ground, and the values of these capacitors are such that the frequency of oscillation will be lowered one semitone from Ab to G.

A blocking and decoupling capacitor CI2II and a load resistor RI22 are connected in series between the plate of triode It@ and ground and the junction between Clit and RI22 is adapted to be connected to a signal collector conductor Hit upon closure of a switch SI. ln a similar manner the signals from the oscillators I2, I3, and I4 may be impressed upon the collector conductor |28 by closure of keying or operating switches S2, S3 and S4 respectively. The collector conductor |26 is connected to the input terminal of the amplifier 90 through a decoupling resistor RIB. While the switches SI, S2, S3, Sli are shown askeying the signal they might he employed to key plate current `to their respective oscillators in the well-known manner, in which case the oscillators would be permanently coupled to the signal collector conductor.

The oscillators I2, I3, and Id are similar to oscillator II except for the slight variations in the values of the components necessary for their different frequencies of oscillation, and similar reference characters have therefore been applied to the corresponding parts which are illustrated, except that the switches for the oscillator I2 corresponding to the switches TI, T2, and T3 have reference characters Td, T5, and Tt applied thereto, the corresponding switches for oscillator I3 bear reference characters Tl, T3, T9 and those for the oscillator lai bear reference characters TIG, TI I, and TI2.

As will appear more clearly hereinafter, by closing proper combinations of the switches SI to S4 and TI to T I 2, four signals, each of any one of four adjacent pitches, may be supplied to the output system of the instrument, and it will be 6 shown that' any of rthe conventional harmonic' chords (except the rarely used 9th chord) in any key may be supplied to the output ampliiier.

In addition to supplying the chord signals, the oscillators II to It are utilized to supply a root bass signal to a pedal bass frequency dividing circuit I Llc. This is accomplished by including, among the combination of switches closed for producing the chord notes, an additional switch, such as BI. This switch is connected to the plate of triode IIlIl through a decoupling resistor RIM and thus may conduct a signal from the oscillator II to a collector conductor M2 which is coupled, through a blocking capacitor Ciad and a series grid resistor RIM, to the grid of a limiting or pulse forming triode HI8. rThis grid is also connected to ground through resistor Rulli and a grid resistor RISII. The plate current is supplied to the triode Idil through a load resistor RI52 connected to a B+ terminal, while the cathode or" this triode is connected to ground.

The output signal of the triode E43 is impressed upon the grid of a rectifying triode |54 through a current limiting and blocking capacitor Citt. The grid of triode lili is connected to ground through a grid resistor Rid@ while the cathode is connected to ground through a conductor itil and a self-biasing resistor Riti?, the latter resistor being by-passed by a capacitor Citt.

The pulse which is sharpened by the limiting tube Iii-il and which is rectified by the triocle ld is impressed upon the grids of alternate pulse responsive frequency divider triodes IGS and Itl through blocking capacitors CIM and Citt'. The grids of these triodes are connected to ground through resistors RIII! and RHI and the plates are connected to B+ terminals through load resistors RIM and RIIE. The grid of triode it is connected to the plate of triode It? through a mesh comprising RI'IS and CIBG in series, having RI82 in parallel therewith. The plate of triocle It is connected to the grid of triode ISI through a similar mesh comprising Rill, CISI, and RI83. As is well-known in the art this interconnection of the grid and plate circuits of these triodes makes one of the tubes nonconducting while the other is conducting plate current, so that when a negative pulse is supplied from the rectifier triode ld, the tube which was conducting is rendered nonconductive by the impression of the negative pulse upon its grid and by the consequent increase in its plate voltage raises the potential of the grid of the other triode suniciently to render it conductive.

The output of triode I 6l is suitably coupled to a rectifier and pulse sharpening triode its which operates in the manner of the triode Ict to supply sharp negative pulses to the input circuits of triodes |92 and |93 Which, with their associated components, constitute a second stage for frequency division. These triodes and their associated circuit components may be the saine as the triodes Ist and IGI and their associated circuit components, except for slight changes of the values of some of the components to adapt the circuits for reliable operation at the lower frequency.

Output signals are derived from the triodes It, It?, and I93 through a conductor 2t@ which is connected to the plates of these triodes through decoupling resistors REM, R2ll2, and Ril respectively. `The signals appearing on the conductor 260 have their high frequencies greatly attenuated and their very low frequencies somewhat attenuated by altering mesh 204 comprising series resistors R206, R201, and R208 and shunting capacitors C210, C211, C212, and C213 and shunt load resistor R214.. The mesh 204 includes a series blocking capacitor C215 connecting it to conductor 200, and the mesh is connected to the input terminal of amplifier 90 through decoupling resistor R218. The resistors R201, R202, and R203 are of graded values such that the amplitude of the signal transmitted through R202 is approximately `onehalf that of the signal provided through R203, and the signal transmitted through R201 is approximately one-fourth of that transmitted through R203. The capacitor C216l and resistor R214 are eiective to attenuate slightly the lowermost frequencies while the remainder of the mesh 2634 attenuates the higher harmonics to a substantial extent.

The switches T1 to T12, S1 to S4, and BI to B4 may be operated in any suitable manner such, for example, as shown in Fig. 2, wherein these switches are conventionally illustrated. Each switch is provided with an actuator bar 230 pivoted on a xed rod 232 and operable by levers 234 pivoted on a xed rod 236. The levers 231i are normally held in their uppermost position against a padded stop 238 by compression springs 240. The levers 230 are similarly resiliently held in their uppermost positions against a suitable limit stop. Each of the levers 234 has a projection 241 for engagement by the enlarged lower end of an accordion type keyboard button 242. These key buttons are mounted for free reciprocation in the keyboard plate 244. Each of the levers 234 is provided with a predetermined combination of downwardly extending projections 246 which are adapted to engage and depress certain of the switch actuating bars 230 thereby causing lugs 2618 of insulating material riveted to these bars to engage and depress the upper switch contact fingers 250 of certain of the switches. The key buttons 242 may be arranged in the conventional manner of an accordion in substantially vertical rows for the dierent musical keys and in horizontal rows for the chords of different character such as the major, minor, '7th, diminished, augmented, minor-117th, and major-l-Gth chords.

It is preferable that the switches T1 to T12 be closed slightly prior to the closure of the S1 to SI1 and B1 to B4 switches to avoid the production of undesirable transients as the oscillator pitch is changed. This may be accomplished by making the lugs 218 for the switches TI to T12 slightly longer than the lugs for the other switches.

Each of the buttons 242 co-operates with only one of the levers 23d and each of these levers differs from all other in the arrangement of the downwardly extending projections 242. For example, the key lever 234 illustrated in Fig. 2 has projections 246 for operating switches T1, T5, S1, S2, S3, and B2, this lever being the one which is operated when the key button 242 for the Bb major chord is depressed. The result of the closure of these six switches is as follows: Closure of switch T1 tunes the oscillator 11 to the pitch F and closure of S1 results in supplying this signal of pitch F from the oscillator 11 to the output system. Closure of switch TB tunes the oscillator 12 to Bb frequency and closure of the switch S2 causes transmission of the signal from this oscillator to the output system of the instrument. Closure ci switch S3 results in transmitting the signal from the oscillator 13, which normally operates at pitch D, to the output system. Thus the tone signals of the notes of the Bb major chord, namely, Bb, D, and F are produced and transmitted to the amplifier 90.

In addition, closure of the switch B2 results in transmission of a signal of Bb pitch from the oscillator 12 to the input of the frequency divider system, causing the latter to transmit to the amplier signals of pitch two octaves lower through R203, one octave lower through R202, and the same pitch through R201. As previously indicated the amplitudes of the signals transmitted through the resistors R201, R202, and R203 are graded so that the tone produced by the frequency divider vsystem will have an apparent pitch two octaves lower than the Bb frequency to which the oscillator 1.2 yhas been tuned by the closure `of switch T6.

It will be noted that tone .signals vof pitch Ab may be produced by either oscillator 1 1 Ior 12, that tones of pitch B may .be produced by either oscillator 12 or 13, that tones of pitch D may be produced by either oscillator 13 or 14 and that tones o pitch F an octave apart may be produced by oscillators 11 and 14.

While in most instances it will be immaterial which oscillator is used to produce the four notes Ab, B, D, and F, each of which may be produced by either two oscillators, there are reasons why it is preferable, when possible, to produce signals Aof these pitches by the use of one of the two possible oscillators. For example, it is preferable that the oscillator 1 1 be used for the production of signals of pitch F in preference to using oscillator 14 since the oscillator I1, with the switch T1 closed, will oscillate one octave lower than the frequency at which the oscillator 14 operates when its switches T10, T11, and T12 are open, and the lower octave note is musically preferable.

Thus when the chord contains a note of pitch F it .is preferable that the signal for this note be produced by closing switches T1, S1, and B1, although it may be produced (an octave higher) by closing S4 and B4. For the pitch Fl switches T2, S1, and BI must be closed. For producing the note G, switches T3, S1, and B1 must be closed. For the production vof a signal of the Ab pitch it is preferable that switch S1 be closed, but it is possible to produce this pitch by closing T4 and S2. Similarly, the following switches are closed for the production ol' signals of other pitches: A, switches T5 and S2; Bb, switches T6 and S2; B, preferably switch S2 but switches Tl and S3 may be used; C, switches T8 and S3; Db, switches TS and S3; D, preferably switch S3, but T10 and S4 may be used; Eb, switches T11 and S4; E, switches T12 and S4.

Assuming that the preferred switches are closed to produce a tone signal for the root of the chord, the switch B1 will be closed whenever the root of the chord is F, Ft, Gr, or Ab, the switch B2 will be closed whenever the root of the chord is A, Bb or B, the switch B3 will be closed whenever the root of the chord is C, Db, or D, and the switch B4 will be closed whenever the root of the chord is Eb or E.

From the foregoing, those skilled in the art may readily produce key levers 234 having the proper number of downwardly extending projections 240 properly located to produce the tone signals necessary for the production of all the chords (except the 9th) together with the pedal root tone signal.

The keyboard for playing the solo section of the instrument may be of any suitable construction, preferably of the pianoforte type with each key arranged to operate the required switches 26 and 32.

In playing the instrument the musician will play the melody, for instance as scored in Fig. 1, on the pianoforte keyboard, and at the points at which a chord is scored will depress the designated chord button 2t?, usually holding this button depressed until the score calls for a rest or the depression of a different chord button. Assuming that a button for a 7th or a diminished chord is depressed, each of the four oscillators l l to le will supply a signal of appropriate pitch to the amplifier' 90 and, in addition, one of these oscillators will supply a signal of pitch corresponding to the root of the selected chord to the frequency dividing circuit Mill. Thus with these four oscillators the tone signals for a full four note chord as well as a root pedal bass tone signal will be supplied to the amplifier. The full melody range of tone signals is supplied from the single oscillator ill so that with these five oscillators it is possible to play very effectively and faithfully as written all popular music and all other music except contrapuntal music and music containing the 9th chord. With the instrument as shown and described herein it is not possible to play the 9th chord because three of the four notes of the 9th chord are separated by but two semitone intervals and do not include the root of the chord. It will be apparent that the four oscillators cannot simultaneously produce the ve different pitches required for a complet-e 9th chord. However, since even in the 9th chord no two notes are adjacent semitones, it will be clear that by the use of six oscillators, each capable of producing two adjacent semitones, the full gamut of the twelve notes in an octave will be available for the production of all of the previously mentioned conventional musical chords. When cost reduction is not controlling, and it is desired to employ six oscillators for the production of all the chords, each of the six oscillators could be identical with the oscillator ll, except that it would be provided with but one additive tuning capacitor, comparable to Cl ill, but of Value that, when connected in the resonant circuit, the oscillator would produce a signal one semitone lower than it produced without such capacitor connected in its tuning circuit. In other respects such an instrument could be the same as the embodiment previously described.

While I have shown and described a particular embodiment of my invention, it will be apparent to those skilled in the art that numerous modiications and variations may be made in the form and construction thereof, without departing from the more fundamental principles of the invention. I therefore desire, by the following claims, to include within the scope of my invention all such similar and modified forms of the apparatus disclosed, by which substantially the results of the invention may be obtained by substantially the saine or equivalent means.

l claim:

l. ln an electrical musical instrument includ-y ing a provision for the playing of many different chords by the manual operation of many control buttons operated one at a time, the combination of an output system including electroacoustic translating means a plurality of electrical oscillators collectively capable of generating electrical musical tone signals of pitches extending lil throughout one octave of the tempered musical scale, and electrical keying switch for each of said oscillators for connecting its output to the output system, a tuning switch for each of said oscillators, a large number of manually operable buttons representing a plurality of chords in a plurality of musical keys, and mechanical linkages connecting each button with some of said keying and tuning switches, said linkages operating a different combination of keying and tuning switches for each of said buttons, each keying switch being operable by a plurality of buttons and each tuning switch being operable by a plurality of different buttons.

2. The combination set forth in claim l, in which said linkages' are proportioned to operate the tuning switches prior to the operation of the keying switches upon depression of the buttons and to operate the keying switches prior to operating tuning switches upon release of the buttons.

3. In an electrical musical instrument capable of playing successively many dinerent chords by the manual operation of many control buttons operated one at a time, the combination of an output system including electroacoustic translating means a plurality of electrical oscillators each tunable to any one of a plurality of musical pitches, an electrical keying switch for each of said oscillators for connecting its output to the output system, a tuning switch for each of said oscillators, a large number of manually operable buttons representing a plurality of chords in a plurality of musical keys, and operating connections between the buttons and said tuning and keying switches, said connections being constructed to operate a different combination of said tuning and said keying switches for each of said buttons such that each keying switch is operable by a plurality of buttons and each tuning switch is operable by a plurality of different buttons.

4. The combination set forth in claim 3 in which said operating connections are proportioned to operate the tuning switches prior to operating the keying switches upon depression of the buttons and to operate the keying switches prior to operating the tuning switches upon release of the buttons.

5. In an electrical musical instrument, the combination of a plurality of oscillators including individual electron discharge devices; a plurality of tuning circuits forming parts of the oscillators respectively; a plurality of tuning switches connected with the tuning circuits of the oscillators respectively for changing their musical pitches to correspond to either of at least two different musical notes; a common output conductor; a plurality of keying switches connected with the oscillators respectively for controlling the effectiveness of the individual oscillators to supply electrical tone signals to the output conductor; a control unit having manually operable control elements corresponding with a plurality of harmonic musical chords in a plurality of musical key signatures; and a selecting mechanism forming a part of the control unit and operable by the control elements to operate selected combinations of the keying switches and the tuning switches to render effective and to tune the oscillators to the notes of the musical chord called for by the control element.

6. In an electrical musical instrument for the rendition of popular and homophonic music having means for producing the melody of such music throughout at least a two octave range, producing the accompaniment, and producing at least a single bass pedal tone; the combination of an oscillator tunable throughout the melody range; an output system; a manual of the pianoforte type including switches operable by the keys thereof for determining the pitch of the oscillator and controlling transmission to the output system of the signals produced by the oscillator; four chord oscillators each tunable to one of at least three adjacent semitone intervals within the accompaniment range; a plurality of chord selecting buttons; button operated switches and circuits completed thereby in predetermined combinations to tune the chord oscillators to the notes of any selected chord and for causing the signals produced by selected oscillators to be transmitted to the output system a bass tone signal related asV the root to the notes of the selected chord.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,332,076 Hammond et al. Oct. 19, 1943 2,497,661 Dome t Feb. 14, 195o 2,505,182 Haller et al. Apr. 25, 1950 

